Laundry prewash stain removers, also known as prespotters, have been in use for several years now. Typically these compositions are available in liquid spray or semi-solid stick form. The consumer applies the stain remover to soiled garments before washing with laundry detergent.
While these pretreatment formulations have demonstrated increased efficacy in cleaning soiled areas over the use of more standard laundry formulations alone, these stain removers have not proved equally viable on all types of stains and fabrics. There are a few reasons why this is true. Current laundry prespotters are based on two mutually exclusive types of technology. Solvent based compositions were formulated to remove tenaceous greasy/oily stains from lipophilic fabric surfaces (polyester and blends of polyester). Aqueous based formulations were developed to remove water-borne stains including those sensitive to oxidation and enzymes.
There are two major reasons why a more universal, aqueous prespotter composition would be desirable. First, efficacy on a wide range of stain types would increase the chances that performance advantages are perceived by the consumer under actual use conditions. Second, environmental pressure on solvents in cleaning compositions has increased significantly in recent years. Regulation of volatile organic carbon (VOC) content in prewash stain removers is under consideration in California (see, e.g., California Regulation to Reduce Volatile Organic Emissions for Consumer Products: Round 1, May 13, 1991.) The trend is toward complete elimination of VOCs from cleaning products.
Unfortunately, the formulation of stable, aqueous based prewash stain removers that are also effective on stubborn oily soils is far from trivial. Certain emulsion type compositions based on nonionic surfactants are quite effective on dirty motor oil stains but are less efficacious on water-borne stains and soils (e.g., grass, grape juice, clay, etc.) The performance of these emulsion based compositions can be improved significantly if builders or chelants are incorporated in the formula. However, many of these chelants are water soluble salts which, when incorporated at desirable levels, cause the emulsion formulation to separate resulting in a heterogeneous, two phase mixture of limited utility.
Alternatively, a hydrotrope can be incorporated in the formula resulting in a clear, single phase composition. The addition of the hydrotrope, though solving the formula stability problem often results in a loss in performance on tenacious oily stains, specifically dirty motor oil. Of course, solvents could be incorporated into these formulations, but this could reduce their environmental acceptability.
Gipp, U.S. Pat. No. 4,595,527, relates to an aqueous laundry prespotter composition containing up to 6% of a chelating agent, a nonionic surfactant (or mixture) and water. The composition can further include up to 1% solvent and have a pH of 4.5 to 12.2. Formulations disclosed in Gipp containing higher levels of chelating agent(s) (.about.6%) were found to be unstable. That is, these compositions were found to separate into two phases when subjected to freeze/thaw stability studies. Attempts to stabilize the formulations of Gipp by incorporation of a hydrotrope resulted in compositions which were significantly less efficacious on oily stains, particularly dirty motor oil. Gipp also fails to disclose propoxylated ethylenediamine and an alpha-olefin epoxide modified polyether thickener as rheology modifiers to improve the stability of the emulsion based formulation.
Ramachandran, U.S. Pat. No. 3,915,633 relates a prewash stain remover composition containing 1 to 20% organic complexing agent, 0 to 30% surfactant and 99 to 50% water. This reference also does not teach the use of rheology modification agents to maintain formula stability while delivering water-borne and oily stain removal properties.
Additionally, thickened aqueous prespotter compositions have been disclosed by Smith et al., U.S. Pat. No. 4,648,987, as well as Ertle, U.S. Pat. Nos. 4,738,791 and 4,738,792.
There presently exists a need in the art for stable aqueous prewash stain removers based on nonionic surfactants, chelating agents and rheology modifiers which can be formulated to deliver outstanding performance on both oily and water-borne stains.